Does anyone have some knowledge about Fluid Mechanics here?In order to get a height of 7 feet I applied the equation V=sq.root(2gh) between the outlet and the maximum height of my stream i.e. 7 feet (2.1336m) and my velocity from this equation was 6.47m/sec at the outlet which eventually produced a Re of more than 120000 and a flow rate of about 300GPHI do have a feeling that my flow rate is correct but what's wrong with my Reynolds number?Someone told me that for open channel flow high Reynolds are acceptable, does anyone have any idea about it?Outlet diameter: 8 mm

The Reynolds number actually has very little to do with the outlet diameter. What you want to calculate is the Reynolds number for the chamber with the straws. That will use the diameter of the internal straws and the velocity of the water as calculated by the cross section area of the external pipe holding the straws.

How the diameter of the outlet plays in to the Reynolds number gets very complicated and beyond the scope of simple equations due to the sudden change in pipe size and internal geometry.